1. Field of the Invention
The present invention relates to a crystallized glass composition which is suitable for use as an insulating material for various types of circuit substrates, a sintered crystallized glass compact obtained by firing the crystallized glass composition, and a circuit substrate using the same.
2. Description of the Related Art
Recently, various types of electronic apparatuses are rapidly miniaturized and the density thereof is being increased by making use of semiconductor integrated-circuit elements, such as ICs and LSIs. Accordingly, there are demands for smaller and denser circuit substrates for mounting the semiconductor integrated circuit elements, etc., and thereby allowing circuit patterns, such as wiring and electrodes, to be increasingly miniaturized and to develop multilayered circuit patterns. Furthermore, as semiconductor integrated-circuit elements with high speed signals are developed, an increase in the speed of signals propagating through circuit substrates is also demanded.
The speed of signals propagating through wiring, electrodes, etc., in a circuit substrate decreases as the relative dielectric constant of an insulating layer formed in the periphery thereof is increased. That is, in order to increase the speed of signals in the circuit substrate, the relative dielectric constant of the insulating layer must be decreased. As circuit patterns are miniaturized and multilayered circuit patterns are formed, insulating layers which ensure superior insulation reliability are also required.
However, the insulating material for forming an insulating layer having a low relative dielectric constant has a lower thermal coefficient of expansion in comparison with a material for forming a circuit pattern, and also has a lower thermal coefficient of expansion in comparison with a dielectric material for forming a dielectric layer having a high dielectric constant and a substrate material, such as alumina. Therefore, when the circuit material, the dielectric material, the insulating material and the substrate material are simultaneously or sequentially fired, deformation, such as warpage and cracking, may occur due to differences in the thermal coefficient of expansion among the individual materials.
In order to overcome the above problem, for example, Japanese Patent Publication No. 2681216 discloses a circuit substrate provided with a dielectric layer having a high dielectric constant in which an insulating layer is formed using an insulating material with a high thermal coefficient of expansion containing MgO, SiO2 and CaO as principal ingredients. The insulating layer has a thermal coefficient of expansion close to that of the dielectric layer having the high dielectric constant and the circuit pattern, and is obtained by preliminarily firing the insulating material containing MgO, SiO2 and CaO as principal ingredients at 1,000xc2x0 C. to 1,300xc2x0 C., and then by firing at 1,240xc2x0 C. to 1,340xc2x0 C. so that a principal crystalline phase of Mg2SiO4, etc., is precipitated.
However, since the insulating material containing MgO, SiO2 and CaO as principal ingredients must be fired at a high temperature of 1,240xc2x0 C. or more as described above, it is not possible to use low-melting point metals, such as Cu and Ag, as materials for forming circuit patterns. Consequently, although high-melting point metals, such as W and Mo, must be used, these high-melting point metals have high resistivities, and thus the requirement for increasing the speed of signals propagating through circuit substrates is not sufficiently satisfied.
To overcome the above described problems, preferred embodiments of the present invention provide a crystallized glass composition which can be fired at low temperatures and which has a low relative dielectric constant after firing, superior insulation reliability and a high thermal coefficient of expansion, and to provide a sintered crystallized glass compact obtained by firing the crystallized glass composition. It is another object of the present invention to provide a circuit substrate in which the deformation is decreased and which can satisfactorily cope with high-speed signals.
One preferred embodiment of the present invention provides a crystallized glass composition comprising: a principal ingredient represented by x SiO2+y MgO+z Al2O3 where x+y+z is 100 parts by weight and the values x, y and z are on lines or within the region enclosed by lines passing through points A (44.0, 55.0, 1.0), B (34.5, 64.5, 1.0), C (35.0, 30.0, 35.0) and D (44.5, 30.0, 25.5) on a ternary diagram thereof; and about 2 to 20 parts by weight of B2O3 relative to 100 parts by weight of the principal ingredient.
Preferably, the values x, y and z are on lines or within the region enclosed by lines passing through points A (44.0, 55.0, 1.0), B (34.5, 64.5, 1.0), E (35.0, 45.0, 20.0) and F (44.5, 35.5, 20.0) on the ternary diagram thereof.
Preferably, the crystallized glass composition of the present invention contains a forsterite crystalline phase (Mg2SiO4) and/or an enstatite crystalline phase (MgSiO3) precipitated when fired at or above the crystallization temperature.
Another preferred embodiment of the present invention provides a sintered crystallized glass compact formed by firing the above described crystallized glass composition at or above the crystallization temperature.
Yet another preferred embodiment of the present invention provides a circuit substrate comprising an insulating layer formed by firing the above described crystallized glass composition at or above the crystallization temperature and a circuit pattern.
Preferably, the circuit pattern is composed of an Ag-based conductive material, a Cu-based conductive material or an Au-based conductive material.
With respect to the crystallized glass composition of the present invention, since the weight ratio of the principal ingredient comprising SiO2, MgO, and Al2O3 lies within the region surrounded by point A, point B, point C and point D in the ternary diagram shown in FIG. 1 and the crystallized glass composition contains about 2 to 20% by weight of B2O3 relative to the principal ingredient, it is possible to perform firing at a low temperature, for example, at 950xc2x0 C. or less, and a low relative dielectric constant, superior insulation reliability and a high thermal coefficient of expansion are exhibited after firing.
Since the sintered crystallized glass compact is formed by firing the crystallized glass composition of the present invention at or above the crystallization temperature, even if firing is performed at a low temperature, for example, at 950xc2x0 C. or less, high sinterability is exhibited, and the sintered crystallized glass compact has a low relative dielectric constant, high insulation reliability and a high thermal coefficient of expansion.
The circuit substrate of the present invention is provided with the insulating layer formed by firing the crystallized glass composition of the present invention at or above the crystallization temperature and the predetermined circuit pattern. Since the insulating layer has substantially the same thermal coefficient of expansion as that of the circuit pattern, the deformation of the substrate, such as warpage and cracking, due to the difference in the thermal coefficient of expansion between the circuit pattern and the insulating layer can be avoided. Since the insulating layer can be fired at a low temperature of 950xc2x0 C. or less, the Ag-based conductive material, the Cu-based conductive material or the Au-based conductive material having a low resistivity can be used as the material for forming the circuit pattern, and since the insulating layer in itself has a low relative dielectric constant, the speed of signals propagating through the circuit substrate can be increased satisfactorily.
Other features and advantages of the present invention will become apparent from the following description of the invention which refers to the accompanying drawings.